The Ocean Margins Program, an interdisciplinary study focussed at Cape Hatteras, is evaluating whether this region is a net source or sink for carbon, while concurrently developing a mechanistic understanding of the production, cycling and fate of organic carbon. Preliminary to a large multi-ship field program in 1996-1997, the first of several short cruises surveyed Cape Hatteras in May 1993.High concentrations of chi a occurred across the shelf. Stations and depths at which chi a was highest also showed elevated concentrations of large phytoplankton, predominantly chained diatoms, but also single-celled dinoflagellates and obligately photosynthetic ciliates. These populations occurred in deeper waters, however, and their abundance was poorly correlated with proxies of community photosynthesis. Instead, small phototrophic nanoplankton, abundant in surface waters, were positively correlated with primary production.Carbon budgets indicated that inner shelf waters contained ca 50% more living POC than outer shelf waters. The relative importance of large phytoplankton and grazers decreased with distance offshore, and they were replaced by photosynthetic nanoplankton and microzooplankton. Even greater changes in living POC occurred in the alongshore direction due to the dramatic reductions in diatoms in southern waters. Estimated herbivory was ca 2-4 gC m(-2) d(-1). The ratio of heterotrophic: autotrophic POC increased from 38% in northern waters to 137% in southern waters, suggesting that phytoplankton was being converted into consumer carbon as shelf waters advected south. The dominant consumers at most stations were single-celled protozoan zooplankton and small copepods, whose fecal products remain in suspension in energetic shelf environments, suggesting that much of the non-diatomaceous POC was exported as shelf waters exited at Cape Hatteras.

Plankton production in the Bay of Villefranche was relatively constant during March and April 1986 but the particle size at which the production occurred was more variable. At the beginning of the study, production was dominated by the larger (ca. 6 μm) flagellates but towards the end it was more or less equally divided between the nano- and picoplankton. There were considerable differences in the estimates of population growth rates, depending on the methods used, but on average the population doubling times were close to 12 hours for autotrophs and 24 hours for heterotrophs. As autotrophs do not grow during the night, each population was therefore doubling once per day. It seemed that each of the nanoor picoplankton populations could adversely affect the growth of the others. This could be either by simple predation or by some form of inhibition. Although nutrient levels in the bay were uniformly low, the addition of nutrients did not always stimulate algal growth. The plankton populations seemed to be both in a state of equilibrium and intense ecological competition.

Seasonal and diurnal patterns of NH4+ and NO3‒ uptake were determined for Lake Kinneret phytoplankton. Nanoplankton generally, but not always, had a higher uptake of NH4+ and NO3‒ than did net plankton. Ammonium was always taken up preferentially and the phytoplankton had lower apparent affinity (Ks) for this ion than for NO3‒. However, during the annual dinoflagellate bloom of Peridinium (February–May), when ambient levels of NH4+ were low and those of NO3‒ were high, a considerable portion of the total N flux was derived from NO3‒. The observed daily fluctuations of specific uptake rates for both NH4+ and NO3‒ can be partially explained by changes in light intensity. The finding that NO3‒ was utilized by the dinoflagellates implies that control of the amounts of this nutrient, which is predominantly supplied from watershed sources, could be important in limiting eutrophication in Lake Kinneret.